Microstructure and mechanical properties of alumina coatings prepared by double glow plasma technique

Low-temperature growth (600 °C) of α-Al2O3 coatings on the stainless steel substrate by double glow plasma technique was achieved. The compositions and microstructures of the coatings prepared at different oxygen flow rates were characterized, respectively, by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectrometry. A phenomenological mechanism for the formation of the Al2O3 ceramic coatings during the oxidation process was proposed on the basis of the experimental results. It was obvious that the oxygen flow rates had a great effect on the surface structure of the prepared Al2O3 coatings. The dense and smooth Al2O3 coatings were prepared at the oxygen flow rate of 15 sccm. In addition, the correlations between the mechanical properties of Al2O3 coating and oxygen flow rates were also discussed. The coating prepared at 15 sccm oxygen flow rate exhibited the best mechanical properties with a maximum hardness of 31 GPa and elastic modulus of 321 GPa. The corresponding critical load of scratch adherence for this sample was 47 N.